Welcome to this community!
Regarding your questions:
I – What are the parameters of the step motors that you recommend for this project?
Do you mean the hardware specifications or the firmware configuration? If you are looking for the hardware specs, you can look at the Stepper Motors section in the Component List & Where to buy page at Thor’s wiki. If you are looking for the firmware configuration, you can check the GRBL source code.
II- I saw on some posts that people bought the PCBs from you. Are you still selling them? How much do they cost?
I still have a few ControlPCBs (just the PCB without the components) available, price is 10€ + shipping cost. At this moment I’m not selling either kits nor assembled boards
III- Could you please provide a list with all the recommended components to buy for this project please?
I think that you are looking for the Component List & Where to buy page at Thor’s wiki 😉
Hope it helps!